To promote the growth of the agricultural economy, delaying plant aging and death while enhancing immune defense abilities can be beneficial. In this study, we focus on AtALMT9, which is located in the vacuolar membrane, and investigates its role in regulating leaf aging and plant disease resistance in Arabidopsis thaliana. We discovered that AtALMT9 negatively regulates leaf senescence and the immune response to pathogenic microorganisms through physiological analysis. The results of RNA-seq and qRT-PCR confirmed the leaf aging and immune-related genes were differentially expressed significantly in almt9 mutants. Furthermore, we found that the leaf senescence acceleration and disease resistance in almt9 mutants are due to the decreased contents of chlorophyll and malic acid as well as the increased levels of salicylic acid (SA) and jasmonate (JA). This study will provide insight into the molecular mechanism of AtALMT9 in regulating plant aging and disease resistance, and serve as a theoretical basis for enhancing agricultural productivity.